The invention relates to a device for carrying out a substantially two-stage linear movement, which is usable preferably, but not only, on a plastics injection molding machine.
A device of this type is known from DE 195 42 453 C2. A shaft with a head with external thread lies in a tube with internal thread. Cylinder or rolling bodies in the form of planets are preferably disposed between shaft and tube, are mounted so as to be non displaceable axially relative to the head and are in operative connection with the two threads of head and tube. Another tube is disposed around the shaft so as to be nor-displaceable relative to this latter and, when the electromechanical unit is displaced, moves into the tube, which is provided with the internal thread, and moves out of the same. The shaft is mounted via cup springs in such a manner that when the shaft is actuated via a first drive unit, it can move just until a greater force is applied, e.g. via a second drive unit. Consequently, the shaft can, where applicable, be separated from the flow of force and the forces are transmitted via the two interlocking tubes, a gradual transfer from the one drive unit to the other is not possible.
Japanese Patent Application JP-A 9-29802 shows a two-stage closing mechanism, where the traveling motion is initially effected via a threaded shaft with a small diameter, whilst the applying of the closing force is then effected via a threaded shaft with a large diameter. The small shaft, to this end, engages via a thread in the large shaft in a coaxial manner. During the traveling motion a nut, which is in operative connection with the external thread of the threaded shaft with the larger diameter, is entrained in a passive manner. When the closing force is to be applied, a sleeve is impinged upon hydraulically, whereby a gap between nut and sleeve is initially closed. With further movement, the nut is pressed by the sleeve into a position, in which the closing force can be applied and the shaft is blocked. Through the thread, however, the point of contact alters depending on the position in such a manner that the result is variable from injection cycle to injection cycle.
Japanese Patent Application JP-A 4-332616, for the traveling motion when the molds are run together, has a ball roller spindle, which plunges into the piston rod of a closing cylinder with the mold in the opened state. For actuating the piston rod of the closing cylinder, there is a ball roller nut disposed at its end, which ball roller nut interacts with the ball roller spindle. To relieve the ball roller spindle, which is not designed for the closing forces, and to apply the closing force, there is an adjusting mechanism provided which is designed so as to be spline-like. On the mold-side end of the closing cylinder and on the end of the closing piston remote from the mold, there are projections provided which slide past one another during the mold closing movement, but which on the other hand are also for transferring the mold forces from the closing cylinder to the closing piston. Consequently, via corresponding auxiliary means, the parts of this locking mechanism are rotated in such a manner that the closing force can then be applied by dosing the gap d. This is also dependent on the position and varies from cycle to cycle.
DE 195 36 565 A1 makes known an electromechanical drive, where also the parts of a threaded rolling planetary spindle are secured via securing means, such as, for example, springs, against passive reversing. There is a two-stage movement, however the rolling bodies are continuously in the flow of force. The second drive unit is not actuated until the first drive unit is secured.
The series closing of the mold of an injection molding machine is known, for example, in EP 0 674 985 A1, where forces are directed both when the displaceable mold carrier is moving to form closure and when the holding force is applied constantly via spindles, which are to be dimensioned accordingly.
WO 92/11993 A1 makes known providing a hydraulic piston cylinder unit with a plunger piston, which at the same time is in operative connection with a threaded spindle. There are no means provided for the effective separating of the threaded spindle from the flow of force.
Proceeding from the state of the art, it is the object of the present invention, in the case of a substantially two-stage linear motional action, to protect the members, which transmit the rotary movement for achieving the straight movement.
This object is achieved through a device for carrying out a substantially two-stage linear movement comprising: a stationary structural unit; a displaceable structural unit; at least one first electromechanical drive unit mounted on the stationary structural unit; at least one shaft rotatably driven by the first drive unit and having a region with an external thread; at least one tube with an internal thread, which tube is disposed coaxially relative to the respective shaft, is displaced with the displaceable structural unit and is in operative connection with the external thread for the displacement of the displaceable structural unit; separating means for a separation of the shaft at least from a further flow of force when at least one predeterminable condition is obtained, the predeterminable condition includes a translatory position of the tube and a predeterminable axial force; and at least one second drive unit, which is actuatable once the predeterminable condition has been achieved, wherein the tube extends through the stationary structural unit and is displaced relative to the stationary structural unit when the first drive unit is actuated, the separating means being jointly displaceable with the second drive unit and, when the predeterminable condition is achieved, the tube is firstly coupled in a detachable manner to the second drive unit and in so doing separates the shaft at least from the further flow of force, which is produced by the second drive unit, as soon as the second drive unit is actuated alone, and that the separating means works radially on the tube.
This object is also achieved through a method for performing a substantially two-stage, linear movement, the method comprising: actuating a shaft by means of at least a first electromechanical drive unit until a predeterminable condition is obtained, the first electromechanical drive unit is mounted on a stationary structural unit; separating the shaft at least from the further flow of force, when the predeterminable condition is achieved, by separating means that work radially on the tube; actuating at least a second drive unit once the predeterminable condition has been achieved, for the displacement of the displaceable structural unit via the tube, which is disposed coaxially relative to the respective shaft, which is displaced with the displaceable structural unit and is in operative connection with the shaft; and displacing the tube relative to the stationary structural unit when the first drive unit is actuated, the separating means being jointly displaceable with the second drive unit and, when the predeterminable condition is achieved, the tube is firstly coupled in a detachable manner to the second drive unit and in doing so separates the shaft at least from the further flow of force produced by the second drive unit, as soon as the second drive unit is actuated alone.
The tube, which has the internal thread, is preferably disposed in such a manner that, on account of the actuation of the first drive unit, the tube is not only displaced relative to the stationary structural unit but also extends through this unit. At the same time, separating means, which are displaceable jointly with the second drive unit, are disposed in such a manner for the separation, where applicable, of the shaft of this first drive unit from the flow of force that, for example, a free movement is possible during the actuation of the first drive unit. However, as soon as, preferably, a predetermined limiting condition occurs, the first drive unit, with the exception of the tube transmitting the forces, can be released. Consequently, the parts of the electromechanical drive unit, which are in operative connection with one another via the threads (head of the shaft, rolling bodies), or alternatively a linear motor forming the first drive unit, are not exposed to the forces from the second drive unit and can accordingly be dimensioned for the transfer of smaller forces. Costly self-locking threads on the electromechanical drive unit are not necessary.